The present invention relates to an amorphous Zr alloy having a large rod-shaped or tubular cross section and a die casting method of manufacturing the amorphous Zr alloy.
Zr alloys have been used as materials for an artificial fiber spinning dies, the filaments of electric lamps and so forth, since the Zr alloys exhibit excellent corrosion resitance, heat resistance and high strength. There are known ZIRCALLOY-2 (Zr-1.5 Sn-0.12 Fe-0.10 Cr-0.05 Ni) and ZIRCALLOY-4 (Zr-1.5 Sn-0.2 Fe-0.10 Cr) for such a purpose.
We have also researched the properties of those Zr alloys. In the progress of our research, we found that the Zr alloy to which a predetermined amount of Al is added togther with Ni, Cu, Fe, Co and/or Mn can be metamorphised to an amorphous state by liquid-quenching, sputtering, atomizing or the like, as disclosed in Japanese Patent Application Laid-Open 3-158446. The amorphous alloy obtained in this way exhibits truly excellent properties such as hardness, strength, bending strength, heat resistance and corrosion resistance. In addition, the alloy is excellent in plastic workability, too, since its supercooled liquid phase exists in the differential temperature range of 50 K or more.
Since the amorphous alloy remarkably reduces its viscosity in the supercooled liquid phase, it is easily shaped to the profile of a product by proper working, e.g. full enclosed die forging, at a temperature zone corresponding to the supercooled liquid phase. In this regard, we have proposed a micromachine gear made of 65% Zr-7.8% Al-7.5% Cu having thickness of a few tens .mu.m, as disclosed in DAI 44-KAI SOSEI KAKOU RENNGOU KOUEN GAIYOU DAI 445-PAGE (The Abstracts of The 44th Combinated Lectures On Plastic Working p. 445).
However, when the amorphous alloy is produced by a single roll method, a twin roll method, a gas atomizing method or the like, there is restriction on the shape of an obtained alloy. That is, the alloy obtained in these ways has the form of thin foil, flake or powder. Consequently, the obtained amorphous alloy is used only for limited purpose accounting industrial efficiency.
There is proposed a method for producing a rod-shaped amorphous Zr alloy, as disclosed DAI 115-KAI NIHON KINNZOKU GAKKAI KOUEN GAIYOU 1994 KOUEN BANGOU 907 (The Abstracts of The 115th Seminar, Japan Metal Society (1994) No.907). The proposed method uses a copper die having an opened upper surface and a rod-shaped cavity. A mother Zr alloy is melted on the copper die by arc heat, and the resultant melt is transferred along the axial direction of the rod-shaped cavity. Hereby, a rod-shaped amorphous Zr alloy is continuously produced.
The copper die proposed in DAI 115-KAI NIHON KINNZOKU GAKKAI KOUEN GAIYOU 1994 KOUEN BANGOU 907 has the rod-shaped cavity whose upper surface is opened. Due to the configuration of the die, it is impossible to control the shape of a cast body which was solidified at the part of the opened upper surface. Consequently, plastic working such as forging, extrusion or press is required in order to reform the cast body to a final shape. Besides, the die has a small surface area coming in contact with the molten Zr alloy due to the opened upper surface, so that the cooling speed of the Zr alloy is not sufficient enough to metamorphise the alloy to the amorphous state. In this point of view, the proposed die is ineffective in the formation of the amorphous state.
By the way, there have been many proposals on the modification of compositions to improve the properties of thin material such as foil or ribbon. However, the results of the researches on said modification of composition are not applicable to the case where a Zr alloy is metamorphised by the die casting method. For instance, cooling conditions are different between the die casting method and the rotary roll cooling method, as follows:
(a) In the die casting method, a molten Zr alloy is cooled from the surface parts in contact with the bottom and the both sides of the die. In the rotary roll cooling method, a molten Zr alloy is cooled unidirectionally from the surface part in contact with the of a roll. PA1 (b) In the die casting method, the molten Zr alloy is kept in contact with the die for a relatively long time. In the rotary roll cooling method, the molten Zr alloy is kept in contact with the roll only for a short time. PA1 (c) In the die casting method, the solidifying condition of the molten Zr alloy is easily influenced by oxygen or the other elements remaining in the molten alloy.
Due to these effects, conventional alloying designs are not suitable for metamorphising the Zr alloy to an amorphous state by the die casting method.